I've said it before and I'll say it again - Cabin Fever, when even the ex-Pink Power Ranger getting naked can't save it from being utterly dire then you know you've got a bad film - there's no real plot, the 'bad guy' is indiscriminate and directionless (much like the script), the characters have a lack of warmth and emotional depth that would shame a parking lot puddle. Essentially just thinking about this film makes me annoyed with how rubbish it was.
(Dis)Honourable mentions go to Freddy Got Fingered and Crazy, Beautiful - the latter being the only film I can remember where I seriously considered just walking out of it, as I later discovered the girl who'd dragged me and my mates there had done.